Conventionally, a wholly aromatic polyimide (trade name “Kapton”) has been known as a material necessary for cutting-edge industries for aerospace and aviation applications and the like. The wholly aromatic polyimide is synthesized from a combination of an aromatic tetracarboxylic dianhydride and an aromatic diamine by utilizing a reaction represented by the following reaction formula (I):
The wholly aromatic polyimide is known to exhibit one of the highest levels of heat resistance (glass transition temperature (Tg): 410° C.) among heat resistance polymers (see Engineering plastics, Kyoritsu Shuppan Co., Ltd., 1987, p. 88 (NPL 1)). However, the wholly aromatic polyimide is colored in brown, because intramolecular charge transfer (CT) occurs between a tetracarboxylic dianhydride unit of an aromatic ring system and a diamine unit of another aromatic ring system. Hence, the wholly aromatic polyimide cannot be used in optical applications and the like, where transparency is necessary. For this reason, in order to produce a polyimide usable in optical applications and the like, research has been conducted on alicyclic polyimides in which no intramolecular CT occurs, and which has a high light transmittance.
There are three kinds of alicyclic polyimides: one is a combination of an alicyclic tetracarboxylic dianhydride and an alicyclic diamine; another is a combination of an alicyclic tetracarboxylic dianhydride and an aromatic diamine; and the other is a combination of an aromatic tetracarboxylic dianhydride and an alicyclic diamine. However, of these alicyclic polyimides, the ones using an alicyclic diamine are difficult to obtain with high molecular weights. This is because an alicyclic diamine has a basicity which is 105 to 106 times greater than that of an aromatic diamine, and hence the polymerization behavior of an alicyclic diamine is totally different from that of an aromatic diamine, so that a salt precipitates during the polymerization. On the other hand, alicyclic polyimides each obtained by combining an alicyclic tetracarboxylic dianhydride and an aromatic diamine can be produced with direct application of general synthetic procedures for the wholly aromatic polyimide, and are easy to obtain with high molecular weights. For this reason, of the alicyclic polyimides, alicyclic polyimides each obtained by combining an alicyclic tetracarboxylic dianhydride and an aromatic diamine have attracted attention in recent years.
Known alicyclic tetracarboxylic dianhydrides used for producing such alicyclic polyimides include those of a monocyclic ring system, a bicyclic ring system, a tricyclic ring system, a tetracyclic ring system, a spiro ring system, and the like. For example, as an alicyclic polyimide using an alicyclic tetracarboxylic dianhydride of a tetracyclic ring system, an alicyclic polyimide is known which is obtained from a dimethanonaphthalene-type tetracarboxylic dianhydride by utilizing a reaction represented by the following reaction formula (II) (see Macromolecules, vol. 27, 1994, p. 1117 (NPL 2)):
In addition, the alicyclic polyimide obtained from the dimethanonaphthalene-type tetracarboxylic dianhydride is also known to exhibit a heat resistance (glass transition temperature (Tg): 404° C.) close to that of the wholly aromatic polyimide (see SAISHIN PORIIMIDO-KISO TO OUYOU- (Current Polyimides-Fundamentals and Applications-), NTS INC., 2002, Chapter 1, alicyclic polyimides, p. 388 (NPL 3)). In addition, as for other alicyclic tetracarboxylic dianhydrides, the followings are disclosed, for example. Specifically, Japanese Unexamined Patent Application Publication No. Sho 55-36406 (PTL 1) discloses 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride. Meanwhile, Japanese Unexamined Patent Application Publication No. Sho 63-57589 (PTL 2) discloses bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydrides. In addition, Japanese Unexamined Patent Application Publication No. Hei 7-304868 (PTL 3) discloses bicyclo[2.2.2]octanetetracarboxylic dianhydrides as raw materials of polyimide resins. Moreover, Japanese Unexamined Patent Application Publication No. 2001-2670 (PTL 4) and Japanese Unexamined Patent Application Publication No. 2002-255955 (PTL 5) disclose 1,2-bis(4′-oxa-3′,5′-dioxotricyclo[5.2.1.02,6]decane-8′-yloxy)ethane. Furthermore, Japanese Unexamined Patent Application Publication No. Hei 10-310640 (PTL 6) discloses bicyclo[2.2.1]heptane-2,3,5-tricarboxyl-5-acetic 2,3:5,5-dianhydride. However, no polyimide having a sufficiently high level of heat resistance can be produced, when an alicyclic polyimide is produced by utilizing any of such conventional alicyclic tetracarboxylic dianhydrides.